More lowlatency optimizations.
skypce
Status: Interested
Joined: 07 Feb 2015
Posts: 11
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Hello Sir, i found some optimizations for the kernel for lowlatency.

Please see the screenshot.:
imageshack.com/i/f01FIA8Tp
The yellow markers are missing features in liquorix kernel. (cpu governor to performance and nohz).
I am testing with ubuntu lowlatency 4.1 kernel.

This is my source:
bitbucket.org/thismaechler/ubuntustudio-14.04-realtimeaudio/
Have a great week. Thank you in advance.
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damentz
Status: Assistant
Joined: 09 Sep 2008
Posts: 1117
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Hi skypce,

The reason why nohz is enabled and the cpu governor is not specifically forced to performance is that they limit the use of the kernel negatively for most users.

For instance, the frequency downscale factor for cpufreq's ondemand is set to 10. The default is 1. This means that cpufreq polls the cpu load 10x less to improve throughput and will also reduce latency in very small corner cases where the load of the system is inconsistent. Also, if you want to, you can configure your system to force performance in userspace using cpufreq or something else related. There's no reason to force performance if the option can be set in realtime by a utility or daemon.

With nohz, it's only nohz idle, not full nohz. This means as soon as there is significant load on the system, your system will poll at 1000hz. Plus, you can actually disable nohz through a kernel parameter if you want to:

:: Code ::
   nohz=      [KNL] Boottime enable/disable dynamic ticks
         Valid arguments: on, off
         Default: on


The defaults in Liquorix are better for most users, a fine trade off for power consumption and traditional desktop use. If you need to reduce OS jitter or run aggressive realtime workloads, you can set the options above in the bootloader or through user space.
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Thank you
skypce
Status: Interested
Joined: 07 Feb 2015
Posts: 11
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Thank you by explain me.
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